Silver corrosion inhibited lubricating composition



United States Patent Ofifice 2,959,546 Patented Nov. 8, 1960 SILVER CORROSION INHIBITED LUBRICATING' COMPOSITION Joseph Versteeg, Roselle, N.J., assignor to Esso Research and Engineering Company, a corporation of Delaware No Drawing. Filed Aug. 28, 1956, Ser. No. 606,565 2 Claims. (Cl. 252 33.4

This invention relates to corrosion inhibitors. Particularly, it relates to the use of formaldehyde and formaldehyde derivatives as silver corrosion inhibitors in lubricating oil compositions containing sulfurized or phospho-sulfurized additives.

The use of various sulfur-containing additives such as sulfurized and phospho-sulfurized compounds in lubricating oil and grease compositions is well-known in the art. These compounds are used as oxidation inhibitors, for inhibiting corrosion of copper-lead bearings and I for boundary lubrication. However, these compounds are very corrosive to silver, which limits their use in many applications. This is particularly true in the application of such additives in lubricants designed for railroad oils, as the sulfurized and phospho-sulfurized additives severely corrode the silver-containing wrist pin bushing in certain types of railroad diesel engines.

It has now been found that formaldehyde and/or any compound which will readily decompose to give free formaldehyde will effectively inhibit the silver corrosion caused by sulfurized and phospho-sulfurized additives, without interfering with the oxidation inhibiting or other desirable properties of these sulfur-containing additives.

The formaldehyde can be added in any form which will give rise readily to the CH O monomer. This includes formaldehyde gas and formaldehyde polymers, such as paraformaldehyde and polyoxymethylenes, which decompose to form formaldehyde on heating or when in an acid environment. Also included are various other formaldehyde derivatives which will readily decompose to produce formaldehyde on mild heating'or-during mild pH variations, such as hemiacetals and acetals of the formula:

RO (CH O R Those formaldehyde derivatives which decompose on a mild change in pH are particularly desirable as they will release formaldehyde as the pH of the oil drops during oxidative degradation to form an acid environment. For example, when an acetal is added to an oil, the change in pH due to oxidation of the oil will slowly decompose the acetal to release formaldehyde and thereby gives a type of formaldehyde bulfering to the lubricant. Mixtures of formaldehyde-containing compounds may also be used, e.g., a mixture of paraformaldehyde and an acetal.

Sulfurized and phospho-sulfurized compounds with which formaldehyde is effective are those generally known to the art as useful as oxidation inhibitors and as copperlead corrosion inhibitors. These include P S or P 8 treated or sulfurized hydrocarbons, esters, alcohols or acids, examples of which are: P 8 treated terpenes and polybutenes; P 8 treated sperm oil; and sulfurized pentenes, dipentenes and phenols. The formaldehyde materials are eifective when the sulfurized or phosphosulfurized additive is used as the only additive, e.g. P 8 treated polybutene; or is supplemented by other additives, e.g. P 5 treated polybutene with barium sulfonate and barium diisobutyl phenol sulfide.

The formaldehyde or formaldehyde producing compound may be added to the lubricating oil or grease composition before or after the addition of the sulfurized or phospho-sulfurized additive, or it may be incorporated into an additive concentrate. These additive concentrates will comprise about 5 to 50 wt. percent mineral oil and about 50 to 95 wt. percent of the sulfurized or phosphosulfurized additive. The formaldehyde producing additive may then be added to the concentrate in amounts equivalent to about 1.0 to 20 wt. percent formaldehyde, based on the weight of the concentrate.

The lubricating oil compositions contemplated by the invention will contain about 0.3 to 20.0 wt. percent, e.g.

- 0.5 to 5.0 wt. percent, of the sulfurized or phosphosulfurized additive; about 0.01 to 1.0 wt. percent, e.g. 0.1 to 1.0 wt. percent, of formaldehyde or formaldehyde equivalent; the remainder of the composition being lubricating oil.

Lubricating oil used in the above compositions may be either a mineral lubricating oil or a synthetic lubricating oil.

Other additive materials may also be added to the various compositions of the invention. Examples of such other additives are other oxidation inhibitors such as phenothiazine, phenyl alpha-naphthylamine; rust inhibitors such as sorbitan monooleate, triethanolamine monooleate; detergents such as calcium sulfonates; load-carrying agents such as tricresyl phosphate; and various other additives. In cases where the final lubricating composition is a grease, then appropriate grease thickeners such as alkali metal soaps of fatty acids may also be added to the composition of the invention.

The invention will be more fully understood by the following examples which are preferred embodiments of the invention.

.. Example I 0.25 wt. percent of paraformaldehyde was added to a base composition containing 3.3 wt. percent of additive A and 96.7 wt. percent of a lubricating oil which was a phenol extracted, clay contacted coastal distillate of SAE 40 grade. Additive A was formed in an oil solution by combining three well known lubricating oil additives; (1) the barium salt of iso-nonyl phenol sulfide described in U.S. Patent 2,362,289, (2) polyisobutene of 1100 molecular weight that had been reacted with 15 wt. percent of P 8 as described in U.S. Patent 2,316,085, and (3) the oil-soluble barium salt of di-dodecyl benzene sulfonic acid. Additive A contained 1.28 wt. percent phosphorus, 8.59 wt. percent barium and 4.18 wt. percent sulfur.

The above oil was tested for silver corrosion according to the EMD Silver Corrosion Test, which involves placing a silver-coated bearing section in the lubricant and heating to 350 F. for 72 hours and then cyanide washing the silver bearing to remove corroded silver and measuring the weight loss of the bearing section.

Various other blends were prepared and tested. Also tested was a commercial lubricant of borderline performance with respect to silver corrosion, in order to demonstrate the highest possible level of silver corrosion that is acceptable for railroad diesel engines. The results of these tests and the compositions used are given in the following table.

' TABLE I Example Material Base Composition 1 .25 wt. percent paraiormaldehyde added to Base Composition.

2.50 wt. percent of C21 x0 alcohol hemil'ormal 2 added to Base Composition.

.25 wt. percent paraiormaldehydeand 1.09 wt. percent of C21 Oxo alc'chol hemiiormal added to the Base Composition.

3.3 wt. percent Additive A combined with .25 wt. percent paraiorrnaldehyde and then added to the oil.

3.3 wt. percent Additive A combined with .50 wt. percent paraformaldehyde and then added to the oil.

.5 Wt. percent Additive 'B 3 added to the Base Composition.

.25 wt. percent paraformaldehyde was combined with 3.3 wt. percent Additive A and then was added to the oil, then 0.5 wt. percent Additive B was added.

.5 wt. percent paraformaldehyde was comned with 3.3 wt. percent Additive A and .4 wt. percent Additive B. This additive mixture was then added to the oil.

Commercial borderline lubricant VII 1 Base Composition is 3.3 wt percent of additive A dissolved in 96.7 wt. percent of a phenol extracted, clay contacted, coastal distlllate lubri eating oil of SAE 40 grade.

2 Tl e On OX0 alcohol hemiformal was formed from a C21 alcohol cut from the products obtained in the OX0 process by the catalytic oxonation 01 a C olefin (tripropylene) with CO and H2 to form a mixture of aldehydes, which are then hydrogenated to form a mixture of highly branched-chain aliphatic primary alcohols.

Adiiti e B is a PzS; treated terpene sold under the trade name Santilube 394-0 which contains about 5.34 wt. percent phosphorus and about 12.63 wt percent sulfur.

As seen from the above table, the base composition had a weight loss of about 66 mg. of silver. The addition of 0.25 wt. percent paraformaldchyde (Example I) sharply reduced the silver corrosion to 27.9 mg. Examples II and III show that a hemiformal and a mixture of paraformaldchyde and hemiformal were also very effective in reducing silver corrosion. Example IV shows that by first combining the phospho-sulfurized additive with the paraformaldehyde and then adding the combined mixture to the lubricating oil (same oil that was used in forming the base composition) an even greater reduction in silver corrosion was accomplished (compare with Example I). Example V was like Example IV, except that it illustrates the use of a higher concentration of paraformaldehyde. The addition of a P S treated terpene (additive B) to the base composition increased the silver corrosion weight loss to 158 mg. However, the addition of .25 wt. percent and .50 wt. percent paraformaldehyde to the oil composition containing both additives A and B, Examples VI and VII respectively, resulted in a very substantial reduction in the silver corrosion of these compositions.

The commercial borderline lubricant showed a weight loss of 48 mg. of silver and illustrates the maximum amount of silver corrosion that will be acceptable in a railroad diesel oil. However, it should be borne in mind that while 48 mgof silver loss in this test would be acceptable, still the life of the silver bearings is considerably shortened by pitting and corrosion.

Additional tests were main a GM 3-71 diesel engine with silver big end connecting rod bearings, thereby giving a dynamic engine test as opposed to the static EMD Test. The results of these additional tests are given in Table II. Both of the following tests were run in the same engine and each test lasted hours.

TABLE II Wt. loss of bearing, mg. Base composition plus .5 wt. percent additive B 1238 Base composition plus .5 wt. percent additive B plus .5 wt. percent paraformaldehydc 415 Base composition and additive B are the same as defined in the footnotes of Table I.

As seen fromTable II, the use of paraformaldchyde causes a substantial reduction in silver corrosion during actual engine operation.

What is claimed is:

1. An improved lubricating oil composition consisting essentially of-a major proportion of a mineral oil, about 0.3 to 20 wt. percent of a conventional sulfur-containing antioxidant selected from the group consisting of mixtures of alkaline earth metal phenol sulfides, alkaline earth metal sufonates and phosphosulfurizcd polyolcfins, and an amount of a formaldehyde-producing compound equivalent to about 0.01 to 1.0 wt. percent formaldehyde based on the total weight of said lubricating oil composition; wherein said formaldehyde-producing compound releases formaldehyde as the pH of said oil drops to form an acid environment during oxidative degradation.

2. The improved lubricating oil composition according to claim 1, wherein said formaldehyde-producing compound is selected from the group consisting of paraformaldehyde and acetals.

References Cited in the file of this patent UNITED STATES PATENTS 2,316,085 Kelso et al. Apr. 6, 1943 2,531,129 Hook et al. Nov. 21, 1950 2,736,706 Morris Feb. 28, 1956 2,736,737 Morris Feb. 28, 1956 2,882,226 Snider April 14, 1959 

1. AN IMPROVED LUBRICATING OIL COMPOSITION CONSISTING ESSENTIALLY OF A MAJOR PROPORTION OF A MINERAL OIL, ABOUT 0.3 TO 20 WT. PERCENT OF A CONVENTIONAL SULFUR-CONTAINING ANTIOXIDANT SELECTED FROM THE GROUP CONSISTING OF MIXTURES OF ALKALINE EARTH METAL PHENOL SULFIDES, ALKALINE EARTH METAL SUFONATES AND PHOSPHOSULFURIZED POLYOLEFINS, AND AN AMOUNT OF A FORMALDEHYDE-PRODUCING COMPOUND EQUIVALENT TO ABOUT 0.01 TO 1.0 WT. PERCENT FORMALDEHYDE BASED ON THE TOTAL WEIGHT OF SAID LUBRICATING OIL COMPOSITION, WHEREIN SAID FORMALDEHYDE-PRODUCING COMPOUND RELEASES FORMALDEHYDE AS THE PH OF SAID OIL DROPS TO FORM AN ACID ENVIRONMENT DURING OXIDATIVE DEGRADTION. 